Ear thermometers have become more common in recent years, replacing mercury and electronic oral thermometers in many clinical and home situations. Ear thermometers work by measuring the temperature of the eardrum (since the medical term for eardrum is "tympanic membrane," these thermometers are sometimes called "tympanic thermometers"). Why the eardrum? The carotid artery that supplies blood to the hypothalamus--the body's temperature control center--passes through the eardrum. Therefore, the temperature of your eardrum corresponds very closely to the core temperature of your body.
Ear or "tympanic" thermometers receive and analyze the radiant heat ("infrared") energy coming from the eardrum. Just as you can feel the heat when you hold your hands up in front of a fire, a tympanic thermometer can detect eardrum temperature without having to actually touch the eardrum by receiving the radiant heat energy coming from the eardrum.
Commercially available tympanic thermometers include a handheld probe device containing a "thermopile" or pyroelectric heat sensor. The sensing probe typically has a tapered or cone shape for easy insertion into the outer ear canal. The heat sensor within the probe picks up the eardrum's radiant heat energy. Microelectronics can determine eardrum temperature from the heat sensor's electrical output.
Most commercially available tympanic thermometers are designed to work with disposable probe covers. Most of these disposable probe covers cover the end of the probe during use with a film such as polyethylene. The film is substantially transparent to infrared radiation but impervious to moisture, ear wax and germs. A different probe cover is used for each patient. Probe covers minimize the risk of spreading disease, and also promote cleanliness and accuracy by preventing ear wax and other secretions from contacting the probe.
A thin film tends to be substantially transparent to the radiation emitted by the eardrum. However, wrinkles in the film can affect its transmissivity. Because the wrinkling pattern may be different from one particular probe cover specimen to another, it is difficult to compensate electronically for wrinkling in the field during the thermometer manufacturing calibration process. It is therefore desirable to eliminate wrinkling as much as possible.
FIGS. 1A-1G show some examples of prior art tympanic thermometer probe covers. These different probe cover designs handle the wrinkling issue in different ways.
The FIG. 1A prior art probe cover 10 is made by Thermoscan, Inc. of San Diego Calif. and comes in a box marked with "U.S. Pat. No. 5,088,834". This probe cover 10 is made out of a single unitary piece of thin, lightweight, semi-rigid, stiff hollow translucent plastic material shaped into a cone 12. The cone 12 includes a thicker "shank" portion 18, and terminates in a thinner end portion 13 comprising an integral piece of thin plastic film 14 that is impervious to moisture but transparent to (and does not absorb) radiant heat energy at the infrared wavelengths emitted by the eardrum. The FIG. 1A one-piece probe cover 10 is designed to be inserted over a correspondingly cone-shaped probe. A surrounding retaining ring base 16 retains cover 10 on the probe during use. When cover 10 is inserted over the probe, plastic film 14 is stretched tightly over the end of the probe to provide a thin, wrinkle-free film "window" that is substantially transparent to infrared radiant energy. The conically shaped stiff "shank" portion 18 of cover 10 tapers to glide into the passageway of a person's ear leading to the eardrum--thus helping to position the probe relative to the eardrum. This stiff construction also allows probe covers 10 to be stacked one inside another for compact shipment.
FIG. 1B shows a prior art probe cover 20 sold by Sherwood Medical Co. This design is explained in U.S. Pat. Nos. 5,980,451; 5,707,343; 5,516,010; 5,293,862; 5,179,936; 4,790,324; 4,662,360 and 4,602,642, and possibly also in a still-pending continuing applications. The FIG. 1B probe cover 20 is intended for use with a tympanic thermometer that senses infrared radiation in an external ear canal of a patient via an IR sensing probe. The IR sensing probe has a forward end, and the thermometer contains an IR sensor spaced from said forward end. The disposable probe cover 20 is said to include a stretchable thin film membrane 28 made of a material which is substantially transparent to IR radiation over a predetermined range of wavelengths. A body portion 22 is said to have an opening sized for having the IR sensing probe inserted therethrough. The thin film membrane 28 is said to extend across the opening in the body portion 22 in an unstretched condition. The membrane 28 is said to be stretchable to remove structural characteristics in the membrane that would interfere with measurement accuracy when the IR sensing probe is inserted through said opening.
To use the FIG. 1B probe cover 20, membrane 28 is positioned adjacent the forward end of the probe of the tympanic thermometer. The membrane 28 is stretched a predetermined amount across the forward end of the probe to remove structural characteristics in the membrane that would interfere with measurement accuracy. The membrane 28 is held stretched over the forward end of the probe, and the forward end of the probe is partially inserted into an external ear canal of a patient with the membrane stretched over the forward end of the probe. The stretched membrane 28 provides a barrier between the patient's external ear canal and the probe of the tympanic thermometer while permitting infrared radiation emitted in the external ear canal to be received by the probe.
The probe cover 30 shown in FIGS. 1C and 1D is manufactured by Welch Allyn Diatek, Inc. of San Diego, Calif. for use with Diatek's InstaTemp Model 9000 tympanic thermometer. See U.S. Pat. No. Re. 34,599. This probe cover 30 is designed to be used with a temperature sensing "gun" also manufactured by Diatek (see U.S. Pat. No. 4,863,281). This probe cover 30 includes a flat paper carrier 32 that supports a piece of transparent polyethylene sheet 34. Sheet 34 is nominally about 0.0005" to 0.001" thick. Sheet 34 is unstretched prior to application on the probe. However, sheet 34 is stretchable, and completely envelopes the probe when cover 30 is placed over the probe--stretching tightly over the probe so as to provide a radiation-transparent film layer between the probe and the patient's ear. Probe cover 30 is automatically dispensed from a vacu-formed plastic cartridge and applied onto the probe during a "cocking" action of the thermometer. The FIG. 1C design has several advantages, including inexpensive construction, flat storage, and stackability.
FIG. 1E represents another prior art probe cover 40 manufactured by Exergen Corp. of Newton, Mass. and comes in packages marked "U.S. Pat. No. 4,993,419." This disposable probe cover 40 comprises a film sheet 42 that is dispensed in a pre-perforated roll. In use, the nurse inserts a pin portion of the ear thermometer positioned opposite the probe into a first ring hole 44, and then wraps film 42 around the front of the probe and continues wrapping until a second ring hold 46 is aligned with the same pin portion. The nurse can then tear sheet 42 from the rest of the roll along the line of perforations 48. Ring holes 44, 46 retain sheet 42 on the probe during measurement. Although probe cover 40 is inexpensive to manufacture, it is difficult for a nurse to position properly onto the probe. In addition, the FIG. 1E probe cover 40 may not always reliably wrap around the front portion of the probe--creating wrinkles that can affect measuring accuracy. The FIG. 1E probe cover 40 can also slip off the probe without the nurse noticing.
FIG. 1F shows a probe cover 90 manufactured by Alaris' IVAC Corporation for the CoreCheck Model 2090 tympanic thermometer (see U.S. Pat. No. 5,066,142). Probe cover 80 includes a rectangular cardboard carrier 92 defining a central circular hole 93. A polyethylene sheet 94 is adhered to cardboard carrier 92 to provide a more or less wrinkle-free window through which infrared radiation may pass. Probe cover 90 is manually slid from a dispenser which holds up to 100 probe covers, onto a platen. In use, the tympanic thermometer probe is pressed through sheet 94 within central circular hole 93 while the platen holds carrier 92 in place. Sheet 94 further stretches over the probe end during this application process, adhering to the conical thermometer.
FIG. 1G shows a still different prior art probe cover design of the present assignee, described in U.S. Pat. No. 5,833,367 (and see also U.S. Pat. No. 5,066,142). This design provides a hollow, tubular body 60 made out of foam. Body 60 terminates in an opening 56. A plastic sheet 58 is prestretched over opening 56 to provide a wrinkle-free window. A narrower portion 50 of the foam body 60 prevents probe 68 from contacting sheet 58 when the probe is inserted into the body. In use, insertion of probe 68 into body 60 may cause the body to expand and sheet 58 to stretch further. Foam body 60 frictionally engages the outer surface 66a of probe 66 to keep the probe cover on the end of the probe without need for any additional retaining mechanism.
For all of the probe covers shown in FIGS. 1A-1G, insertion of the sensing probe into the probe cover causes a plastic sheet to stretch. For the probe covers shown in FIGS. 1A-1E, a plastic sheet goes from an unstretched condition to a stretched condition. For the probe covers shown in FIGS. 1F and 1G, the sheet goes from a prestretched condition to a further stretched condition. In all cases but the FIG. 1G probe cover, the plastic sheet is stretched over the probe end.
Stretching the plastic sheet or film upon application of the probe cover to a probe can cause problems. For example, one common problem is tearing of the sheet or film. There is a risk of cross-contamination if the sheet tears. There is also a risk that ear wax or other secretions will get on the lens commonly found at the extreme forward end of the probe. Such substances can partially occlude the sensing probe optical path, leading to inaccurate temperature measurements. Despite manufacturers' efforts to educate clinicians to clean the lens, few clinicians actually perform this task.
Another problem with stretching the plastic sheet or film over the probe is that the sheet will tend to adhere to the probe. This can make it more difficult to strip off the probe cover after a measurement.
Still another problem is that stretching the plastic sheet in the field leads to different amounts of stretching depending on the technique a nurse or other care-giver uses to apply the probe cover to the probe. For example, certain of these probe covers are stretched by an amount that depends on the clinician's application of uncontrolled force levels during probe cover application. Non-uniform or non-consistent stretching can lead to measurement inaccuracies.
Thus, while substantial work has been done in the past in this area, further improvements are possible.
The present invention solves these problems by providing a plastic sheet that is prestretched and does not stretch further upon application of the probe cover to the probe.
In accordance with the present invention, a substantially non-stretchable structure is provided on or adhered to the film in the area where the probe contacts the film. This additional structure is designed so that it does not occlude infrared radiation from reaching the probe while maintaining the film in a prestretched, wrinkle-free condition and preventing the film from stretching further.
In one particular example embodiment, the structure may comprise a concentric registration ring that is adhered to the film. The registration ring includes a central open hole portion through which infrared radiation may pass without occlusion. When the probe cover is applied to the probe, the probe contacts the ring. Since the ring is substantially non-stretchable, the ring prevents the film from further stretching over the probe. Further, in the preferred embodiment, the ring self-adheres to the film--maintaining the film in a prestretched, wrinkle-free condition.
The additional structure provided by the present invention helps to minimize the likelihood that the film will tear over the thermometer's probe tip. An additional benefit is that the structure reduces the surface adhesion of the film to the probe, improving or easing the probe cover ejection process after a measurement. Further, by pre-stretching the film during manufacturing with a highly repeatable process, the transmissivity of the film is inherently very consistent from one probe cover to the next .